The present invention relates to a position transducer comprising a coil supplied by a source of alternating current in which a core the position of which has to be measured is capable of being axially shifted.
Such a position transducer is described in U.S. Pat. No. 3,688,187. The measuring coil is connected in one of the branches of a measuring bridge, the other branches of which comprises resistances. For temperature compensating the transducer, a temperature dependent resistance is connected in one of the branches of the bridge. This resistance only provides a good compensation in a relatively limited temperature range but does not permit utilization of the transducer at high temperatures. U.S. Pat. No. 4,667,158 describes a position transducer which outputs on the principle of eddy currents, the coil being connected in one branch of a measuring bridge. Like the transducer in CH 509,373 the transducer can be temperature compensated only in a relatively limited range of temperatures and it is not foreseen for working at high temperatures.
Generally speaking, one compensates for temperature dependency of a transducer by a differential measurement of the variation of the impedance of the coil as a function of the position of the core inside of the coil. However, such a differential measurement necessitates a set of coils arranged axially side by side, the overall length being practically three times as great as the length of a single measuring coil used in a direct, non-differential measurement. It is clear that according to the application, it would be useful to reduce not only the space taken by the transducer but also its weight. This is more particularly the case in aeronautical applications where the transducer can be used e.g. for measuring the inclination of the blades which determine the orientation of the flow of air provided by a distributor to a turbine or for measuring the inclination of the flaps of the elevators. In the first application, measurement of the inclination of the blades, the transducer must operate at temperatures of up to +250.degree. C. In the second application, the transducer must operate at an ambient temperature which may be as low as -40.degree. C. Therefore, it would be useful to have a position transducer of light weight and small dimensions capable of operating between -40.degree. C. and +250.degree. C. with a good stability as a function of temperature and, does not require a differential arrangement in order to simplify the transducer and reduce the costs thereof.